The establishment of long term cultures of postnatal mouse liver epithelial cells should now be possible, since we have identified conditions for (1) cell isolation, (2) cell attachment to substrate, (3) basic medium composition, and (4) hormonal supplements. Establishment of cell lines from mouse fetal liver took about 17 months, so we may expect the comparable work with postnatal livers to extend over many months. We shall in the meanwhile examine the behavior of other normal and neoplastic mouse cells in defined culture media, both autoclavable and buffered with non-volatile buffers, and conventional, buffered with bicarbonate. We shall attempt to adapt media to specific cell types, e.g., leukemias, erythroid cells, teratocarcinoma cells, etc. Adaptation will be by means of variations in buffer systems, pH, ion balance, osmolality, redox potential, inclusion of hormones and application of cell attachment factors. We shall utilize some of the cell sytems that we already have in operation for studies of cell interaction, e.g. by co-cultivation of fetal or postnatal liver cells with cells from the endocrine pancreas of normal and diabetic mice. BIBLIOGRAPHIC REFERENCES: Dunham W.B., and C. Waymouth. 1976. Intradermal transplantation in mice of small numbers of sarcoma cells followed by tumor growth and regression. Cancer Res. 36:189-193. Eppig, J.J., E.H. Leiter, and C. Waymouth. 1976. Culture of cells in BEEM capsules: a new technique for electron microscopic study of monolayer cultures. In Vitro 12:65-73.